Direct detection and spectral characterization of extra-solar planets is one of the most exciting but also one of the most
challenging areas in modern astronomy. The challenge consists in the very large contrast between the host star and the
planet, larger than 12.5 magnitudes at very small angular separations, typically inside the seeing halo. The whole design
of a "Planet Finder" instrument is therefore optimized towards reaching the highest contrast in a limited field of view and
at short distances from the central star. Both evolved and young planetary systems can be detected, respectively through
their reflected light and through the intrinsic planet emission. We present the science objectives, conceptual design and
expected performance of the SPHERE instrument.

/pdf/sphere-a-planet-finder-instrument-for-the-vlt-3fpbro30lz.pdf

SPHERE: A ‘Planet Finder’ Instrument for the VLT

Roughness determines many functional properties of surfaces, such as adhesion, friction, and (thermal and electrical) contact conductance. Recent analytical models and simulations enable quantitative prediction of these properties from knowledge of the power spectral density (PSD) of the surface topography. The utility of the PSD is that it contains statistical information that is unbiased by the particular scan size and pixel resolution chosen by the researcher. In this article, we first review the mathematical definition of the PSD, including the one- and two-dimensional cases, and common variations of each. We then discuss strategies for reconstructing an accurate PSD of a surface using topography measurements at different size scales. Finally, we discuss detecting and mitigating artifacts at the smallest scales, and computing upper/lower bounds on functional properties obtained from models. We accompany our discussion with virtual measurements on computer-generated surfaces. This discussion summarizes how to analyze topography measurements to reconstruct a reliable PSD. Analytical models demonstrate the potential for tuning functional properties by rationally tailoring surface topography - however, this potential can only be achieved through the accurate, quantitative reconstruction of the power spectral density of real-world surfaces.

/pdf/quantitative-characterization-of-surface-topography-using-1di6n32wn5.pdf

Quantitative characterization of surface topography using spectral analysis

The SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) planet finder instrument for ESO's VLT
telescope, scheduled for first light in 2011, aims to detect giant extra-solar planets in the vicinity of bright stars by the aid
of an extreme-AO turbulence compensation system and to characterize the objects found through spectroscopic and
polarimetric observations. Dual imaging observations within the Y, J, H and Ks atmospheric windows (~0.95 - 2.32μm)
will be done by the aid of the IRDIS cryogenic camera. We describe briefly the science goals of IRDIS and present its
system architecture. Current status of the instrument design is presented, and expected performance is described in terms
of end-to-end simulations.

The infra-red dual imaging and spectrograph for SPHERE: design and performance

Concentrating photovoltaic (CPV) systems are a key step in expanding the use of solar energy. Solar cells can operate at increased efficiencies under higher solar concentration and replacing solar cells with optical devices to capture light is an effective method of decreasing the cost of a system without compromising the amount of solar energy absorbed. However, CPV systems are still in a stage of development where new designs, methods and materials are still being created in order to reach a low levelled cost of energy comparable to standard silicon based PV systems. This article outlines the different types of concentration photovoltaic systems, their various design advantages and limitations, and noticeable trends. This will include comparisons on materials used, optical efficiency and optical tolerance (acceptance angle). As well as reviewing the recent development in the most commonly used and most established designs such as the Fresnel lens and parabolic trough/dish, novel optics and materials are also suggested. The aim of this review is to provide the reader with an understanding of the many types of solar concentrators and their reported advantages and disadvantages. This review should aid the development of solar concentrator optics by highlighting the successful trends and emphasising the importance of novel designs and materials in need of further research. There is a vast opportunity for solar concentrator designs to expand into other scientific fields and take advantage of these developed resources. Solar concentrator technologies have many layers and factors to be considered when designing. This review attempts to simplify and categorise these layers and stresses the significance of comparing as many of the applicable factors as possible when choosing the right design for an application. From this review, it has been ascertained that higher concentration levels are being achieved and will likely continue to increase as high performance high concentration designs are developed. Fresnel lenses have been identified as having a greater optical tolerance than reflective parabolic concentrators but more complex homogenisers are being developed for both system types which improve multiple performance factors. Trends towards higher performance solar concentrator designs include the use of micro-patterned structures and attention to detailed design such as tailoring secondary optics to primary optics and vice-versa. There is still a vast potential for what materials and surface structures could be utilised for solar concentrator designs especially if inspiration is taken from biological structures already proven to manipulate light in nature.

/pdf/optics-for-concentrating-photovoltaics-trends-limits-and-3ddbtiv50v.pdf

Optics for concentrating photovoltaics: Trends, limits and opportunities for materials and design

Roughness determines many functional properties of surfaces, such as adhesion, friction, and (thermal and electrical) contact conductance. Recent analytical models and simulations enable quantitative prediction of these properties from knowledge of the power spectral density (PSD) of the surface topography. The utility of the PSD is that it contains statistical information that is unbiased by the particular scan size and pixel resolution chosen by the researcher. In this article, we first review the mathematical definition of the PSD, including the one- and two-dimensional cases, and common variations of each. We then discuss strategies for reconstructing an accurate PSD of a surface using topography measurements at different size scales. Finally, we discuss detecting and mitigating artifacts at the smallest scales, and computing upper/lower bounds on functional properties obtained from models. We accompany our discussion with virtual measurements on computer-generated surfaces. This discussion summarizes how to analyze topography measurements to reconstruct a reliable PSD. Analytical models demonstrate the potential for tuning functional properties by rationally tailoring surface topography—however, this potential can only be achieved through the accurate, quantitative reconstruction of the PSDs of real-world surfaces.

/pdf/quantitative-characterization-of-surface-topography-using-45kh8tzr33.pdf

Surface topography and light scattering were measured on 15 samples ranging from those having smooth surfaces to others with ground surfaces. The measurement techniques included an atomic force microscope, mechanical and optical profilers, confocal laser scanning microscope, angle-resolved scattering, and total scattering. The samples included polished and ground fused silica, silicon carbide, sapphire, electroplated gold, and diamond-turned brass. The measurement instruments and techniques had different surface spatial wavelength band limits, so the measured roughnesses were not directly comparable. Two-dimensional power spectral density (PSD) functions were calculated from the digitized measurement data, and we obtained rms roughnesses by integrating areas under the PSD curves between fixed upper and lower band limits. In this way, roughnesses measured with different instruments and techniques could be directly compared. Although smaller differences between measurement techniques remained in the calculated roughnesses, these could be explained mostly by surface topographical features such as isolated particles that affected the instruments in different ways.

/pdf/surface-characterization-techniques-for-determining-the-root-1bn2vivtpm.pdf

Surface characterization techniques for determining the root-mean-square roughness and power spectral densities of optical components

The invention relates to a method for reduction of gas-generated light absorption and light dispersion and/or contamination on using light at an applied wavelength of below 200nm in optical beam paths. The above is achieved, whereby the gases located in the beam path are at least partly evacuated to a sub-atmospheric pressure and simultaneously, or subsequently, a flushing gas is introduced into the beam path, whereby despite the introduction of said flushing gas, the sub-atmospheric pressure is retained and the total absorption in the beam path treated thus comprises at most 50 %.

Jörg Steinert

Papers

Surface characterization techniques for determining the root-mean-square roughness and power spectral densities of optical components

Method and device for suppression of light absorption, light dispersion and contamination with wavelengths below 200nm